This invention relates to lifts. More particularly, it relates to wheel chair lifts for vehicles.
Lift mechanisms which enable large and/or unwieldy articles to be transferred into and out of vehicles have been in existence for some time.
A number of lifts have been adapted for passenger vehicles to provide access for people with handicaps. Most of the prior art wheelchair lifts which are stowable on the exterior of vehicles require relatively extensive track systems or support structures on the undercarriage of the vehicles. These extensive tracks and support systems add weight to the vehicle and take up substantial amounts of space which limits their usage to certain full size vans or other large vehicles.
The prior art wheelchair lifts, which do not utilize the track systems or extensive support structures will typically provide attachment points that are quite close to each other on the wheelchair platform. This can cause stability problems and extreme stress in the areas of attachment between the platform and the lifting links. Attempts to increase the stability and rigidity such as by providing reinforcing structure on the platform will necessarily increase the weight which will be raised and lowered requiring more power and thus stronger and heavier structures for supporting the up and down drive lifting means. Examples of prior art lifts follows.
U.S. Pat. No. 3,263,835 to Lugash discloses a lift that is rotatably attached to an undercarriage of a truck. The lift comprises a platform which is raised or lowered by two sets of rotatable "pantographic" arms located at the sides of the platform and which are concurrently actuated by a hydraulic cylinder. This lift takes up a substantial amount of vertical space and thus would be difficult to use as a wheelchair lift mounted below the undercarriage on modern mini-vans.
U.S. Pat. No. 4,711,613 to Fretwell discloses a wheelchair lift rotatably attached to an undercarriage of a vehicle. The lift comprises a platform which is raised or lowered by a pair of adjacent parallel links located at one side of the platform. Power to the parallel links is provided by a hydraulic cylinder one end of which is attached to one of the parallel links, the other end of which is attached to the rotational support assembly. The platform is attached to the links at a centrally positioned region at two points quite close to each other on the side of the platform. This may cause operating difficulty or instability, particularly when the weight of the wheelchair is forward or rearward on the platform.
Another lift which is rotatably attached to a vehicle is disclosed in U.S. Pat. No. 4,026,387 to Abreu. In Abreu, a platform is attached at one corner to a dual purpose mechanism which is attached to an exterior side of a vehicle adjacent a door opening. The dual purpose mechanism raises and lowers the platform by means of powered telescoping shafts which serve to raise and lower the platform. The dual purpose mechanism also permits the platform to be rotated between operative and storage position. When the platform is in its stored position, the top surface of the platform abuts the undercarriage of the vehicle and frictionally retains the lift in its storage position. Again, the closely spaced attachment points of the lift mechanism to the platform can create operating and stability problems particularly when the weight of the wheelchair is distally positioned on the platform.
Another type of lift is disclosed in U.S. Pat. No. 4,134,504 to Salas. In Salas, a lift is attached to an undercarriage of a vehicle and is horizontally extended and retracted between operative and storage positions by a somewhat complex cable system. The lift comprises a platform which is raised or lowered by two sets of parallel arms located at the sides of the platform, and which are concurrently actuated by a hydraulic cylinder. Only one of the parallel arms of each set is powered.
Yet another type of lift is disclosed in U.S. Pat. No. 5,556,250 to Fretwell. The Fretwell '250 is similar to the Salas lift mechanism in that Fretwell '250 provides two sets of parallel arms located at the sides of a platform, the parallel arms are concurrently actuated by a hydraulic cylinder, and the lift mechanism is linearly extended and retracted between operative and storage positions by a complex gear and chain driven track system. Fretwell '250 also discloses an enclosure, attachable to the undercarriage of a vehicle into which the lift mechanism is positioned for storage.